As a display method for displaying, on a display screen, a plurality of pieces of content data such as a still image and a moving image, a display method called thumbnail display or index display has been known. For example, in an index display method disclosed in Patent Literature 1, when a plurality of pieces of image data are displayed on a TV monitor or the like, pieces of image data having the same aspect ratio are selected. Then, reduced images of the pieces of image data thus selected are simultaneously index-displayed on a TV monitor. At this time, depending on the aspect ratio of the pieces of image data displayed on the TV monitor, the number of pieces of image data to be displayed is appropriately changed. Accordingly, it is intended that more information is simply displayed in a limited display space (e.g., paragraphs [0022] to [0032] in the specification of Patent Literature 1).